Controlling movement of a vessel traveling through water during a seismic survey operation

ABSTRACT

To perform control of movement of a marine vessel traveling through water during a seismic survey operation, input information relating to factors that affect a speed of the marine vessel is received. The speed of the marine vessel is adjusted in response to the received information relating to the factors that affect the speed of the marine vessel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/956025 filed Dec. 13, 2007, which is incorporated herein by referencein its entirety.

TECHNICAL FIELD

The invention relates to controlling movement of a vessel travelingthrough water during a seismic survey operation, which includesadjusting a speed of the vessel.

BACKGROUND

Seismic surveying is used for identifying subterranean elements, such ashydrocarbon reservoirs, fresh water aquifers, gas injection reservoirs,and so forth. In a marine seismic surveying operation, seismic sourcesand seismic sensors are towed by one or more marine vessels, with theseismic sources and sensors towed through a body of water above a seafloor. The seismic sources are activated to generate seismic wavesdirected into the subterranean structure. Examples of seismic sourcesinclude air guns, vibrators, explosives, or other sources that generateseismic waves.

The seismic waves generated by a seismic source travel into thesubterranean structure, with a portion of the seismic waves reflectedback to the surface for receipt by seismic receivers (e.g., geophones,hydrophones, etc.). These seismic receivers produce signals thatrepresent detected seismic waves. Signals from seismic receivers areprocessed to yield information about the content and characteristic ofthe subterranean structure.

Conventionally, inline positioning of a marine vessel towing a seismicspread (which can include seismic sensors and/or seismic sources) isperformed manually by an operator adjusting the throttle on the bridgeof the marine vessel. Inline positioning refers to positioning of themarine vessel along the direction of movement of the marine vessel forperforming the seismic survey operation. However, performing the inlinepositioning of a marine vessel manually is typically inaccurate and doesnot take into account various environment factors, such as the specificvessel, the spread being towed by the vessel, and environment impact ofsea waves and wind.

SUMMARY

In general, according to an embodiment, a method of controlling movementof a vessel traveling through water during a seismic survey operationincludes receiving information relating to constraints representingplural aspects of a system for performing the seismic survey operation.A speed of the vessel is adjusted in response to received informationrelating to constraints representing plural aspects of a system forperforming the seismic survey operation.

Other or alternative features will become apparent from the followingdescription, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example arrangement that includes multiple vesselstowing respective seismic spreads.

FIG. 2 is block diagram of a feedback controller for adjusting speed ofa marine vessel, according to an embodiment.

FIG. 3 is a block diagram of a feedforward controller for adjusting aspeed setting based on various input information, according to anembodiment.

FIG. 4 is a flow diagram of an automated process of controlling movementof a marine vessel, according to an embodiment.

FIG. 5 is a flow diagram of an automated process of controlling movementof multiple marine vessels, according to an embodiment.

FIG. 6 is a block diagram of a computer in which control software isexecutable to control movement of a marine vessel, according to anembodiment.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providean understanding of the present invention. However, it will beunderstood by those skilled in the art that the present invention may bepracticed without these details and that numerous variations ormodifications from the described embodiments are possible.

FIG. 1 illustrates an example arrangement for performing a marineseismic survey operation, where the example arrangement includes fourmarine vessels 102, 103, 104, and 106 that move through a body of water100. The marine vessel 102 can tow a seismic spread 108 that includesstreamers 110, where each streamer 110 carries multiple seismic sensors.Similarly, the marine vessel 103 can tow a seismic spread 109 thatincludes streamers 111, where each streamer 111 carries multiple seismicsensors. Each of the marine vessels 104 and 106 tows a respective string112 and 114, respectively, of seismic sources, which can be air guns,explosives, vibrators, or other acoustic sources.

During the seismic survey operation, the seismic sources are activatedto generate seismic signals that are directed through the sea water intoa subterranean structure under a sea floor (not shown). Reflectors(e.g., hydrocarbon reservoirs, water aquifers, gas injection reservoirs,etc.) in the subterranean structure reflect portions of the seismicsignals, with the reflected seismic signals being received by theseismic sensors on the streamers 110. From the information detected bythe seismic sensors, the subterranean structure can be characterized.

As further depicted in FIG. 1, each of the marine vessels 102, 103, 104,and 106 includes a respective computer 116, 117, 118, and 120. Inaccordance with some embodiments, the computers 116, 117, 118, and 120are used to perform automated control of inline movement of the marinevessels through the water 100. In a different embodiment, instead ofcontrolling inline movement of multiple vessels, techniques according tosome embodiments can be used to perform control of inline movement ofjust a single vessel. “Inline movement” refers to the movement of avessel along a direction in which seismic surveying is to be performed.

The activation of the seismic sources is according to a predefined trackalong the sea floor. If environment factors should affect the positionof the marine vessel with respect to desired positions of the marinevessel over the sea floor, the vessel speed should be adjusted. Also, itis desired that the surveying be performed as quickly as possible (withthe marine vessel traveling at higher speeds), to enhance seismicprocessing speed. In accordance with some embodiments, automated controlof movement of vessel takes into account information relating to variousconstraints representing plural aspects of a system that performs theseismic surveying operation. The various aspects of the system caninclude, as examples, the following: (1) tension of streamers, such asstreamers 110, and 111 towed by a marine vessel; (2) warmup time forseismic sources, such as the seismic sources carried on strings 112 and114; (3) the stability of deflecting structures, such as monowings onstreamers for spreading streamers apart; and (4) minimum time betweenshots (activations of seismic sources) to satisfy data processing timeneeded between activations of seismic sources and to avoid overlap ofdata recordings across multiple activations. The various constraintsnoted above are constraints on the speed of a vessel.

In addition, the automated control of the movement of a marine vesselcan also take into account the present speed of the vessel, as well asinline sea currents, winds, waves, and so forth. The constraints andsome of the other inputs listed above are examples of factors thataffect the speed of the marine vessel.

In some embodiments, input information relating to the factors thataffect the speed of a marine vessel are fed into one or more feedforwardcontrollers implemented by a computer (116, 117, 118, and/or 120), forexample. The feedforward control based on the various factors is used bythe feedforward controller(s) to adjust a speed setting of the vessel.The speed setting adjustment is performed such that the vessel will beat a correct position when a discrete seismic event is to occur, wherethe seismic event can be activation of a seismic source or recording ofa reflected signal due to activation of the seismic source. The positionof the vessel refers to the inline position of the vessel defined in thex-y plane that is generally parallel to the sea floor. For example, itmay be desirable to perform a shot (activation of a seismic source)every 25 meters. To accomplish this, the speed setting of the vessel isadjusted, taking into account the various speed factors, such that thevessel is properly positioned when a shot occurs.

In addition to the feedforward control based on the various factorsabove to adjust the speed setting, feedback control can also beperformed by the computer (116, 117, 118, 120) to maintain the speed ofthe vessel at the speed setting. The speed of a vessel can be measuredusing any one or more of the following: GPS (global positioning system)receivers, vessel relative water flow measurement devices, and so forth.By combining the feedback control with the feedforward control, inlinedeviation of a vessel from a predefined plan or track for performing aseismic operation can be minimized or reduced. By using the feedforwardcontrol based on the various input information noted above, the speedsetting of a vessel can be optimized, where the speed setting is set ashigh as possible, while not violating the constraints, to enhance thespeed at which a marine seismic survey can be performed.

The above describes automated control of vessel speed for a singlevessel. Techniques according to some embodiments can also be applied toa multi-vessel arrangement, in which it is desirable to maintain thesame speed for all vessels in the arrangement. The master vessel (suchas the vessel 102 and/or 103 towing the streamers 110 and/or 111)maintains a particular speed (subject to the changes in speed setting asdiscussed above), while the other vessels 104, 106 (referred to as“slave vessels”) try to position themselves inline with respect to themaster vessel. The slave vessels (e.g., 104, 106) can adjust their speedbased on movement of the master vessel (as discussed in further detailbelow), as well as based on a position of each slave vessel along apredefined track.

FIG. 2 shows an example feedback controller 200 that can be implementedby a computer, for example. In one example embodiment, the feedbackcontroller is a PID (proportional-integral-derivative) controller.Alternatively, the feedback controller can be a P (proportional)controller, or a PI (proportional-integral) controller. The P, PI or PIDprocessing is performed by a processing module 202. In yet anotheralternative, the feedback controller can be a Kalman filter withmultivariable control or model predictive control. The input to theprocessing module 202 is an output of a summer 204, which has a positiveinput to receive the speed setting of the vessel, and a negative inputto receive the output (speed of vessel) of the processing module 202. Byusing the feedback controller 200 according to an embodiment, the speedof the vessel can be maintained to keep the vessel at the given speedsetting.

The speed setting can be speed over ground (SOG) and/or speed throughwater (STW). Following a reasonable SOG setting will ensure that theconstraint relating to warmup time for the seismic sources and theminimum time between activations of seismic sources are satisfied. Usingan STW setting will allow constraints relating to the tension of thestreamers and the stability of deflecting structures (e.g., monowings onstreamers) to be satisfied.

The speed setting that is provided as an input to the feedbackcontroller 200 of FIG. 2 can be set (adjusted) by a feedforwardcontroller 300, as depicted in FIG. 3. The feedforward controller 300can be a multivariable feedforward controller that can receive as inputmultiple variables (A, B, C, D, E, F, G, H in the illustrated example)to provide an optimal speed setting at its output. Examples ofmultivariable feedforward controllers that can be used include Kalmanfilters, neural networks, and so forth. Alternatively, instead of usinga multivariable feedforward controller, multiple single-loop feedforwardcontrollers, each for receiving a respective one of the inputs A-H, canbe used, for adjusting the speed setting of the vessel.

The inputs A-H to the feedforward controller 300 can be as follows:

-   -   A: information relating to tension of the streamers;    -   B: information relating to warmup time for the seismic sources;    -   C: information relating to stability of deflecting structures on        the streamers;    -   D: minimum time between activations of seismic sources;    -   E: actual vessel speed;    -   F: inline current of the water;    -   G: wind speed; and    -   H: one or more other vessels (such that relative positions of        master and slave vessels can be maintained, for example).

Note that other or alternative input information can be fed into thefeedforward controller 300 for adjusting the speed setting.

In an alternative embodiment, instead of using feedback and feedforwardcontrollers as discussed above, a different control structure, such as amodel predictive control structure, can be used. Such a differentcontrol structure can have the constraints integrally with the controlalgorithm performed by the control structure.

FIG. 4 shows a general flow diagram of a procedure for performingsingle-vessel control using some embodiments of the invention. Automatedcontrol is provided, such as automated control using a computer. Theprocedure involves performing (at 402) feedforward control based onvarious inputs (at discussed above) to adjust the speed setting of thevessel. Also, the procedure involves performing (at 404) feedbackcontrol to maintain the vessel at the speed setting adjusted by thefeedforward control.

FIG. 5 shows a multi-vessel control procedure for performing control ofmovement of multiple vessels. In one embodiment, one of the vessels,such as the vessel towing the streamers, is identified as the mastervessel. Note that there can be plural master vessels (such as two mastervessels 102 and 103 in FIG. 1). Thus, reference to “master vessel” belowis intended to cover a multi-master vessel scenario. The master vessel,using its computer, performs (at 406) control of the speed of the mastervessel according to the single-vessel control procedure of FIG. 4. Theremaining vessels are slave vessels.

The slave vessels perform (at 408) feedforward control based on theactual speed of the master vessel for adjusting the speed setting of theslave vessels. In other words, if the computer on a slave vessel detectsthat the slave vessel is moving at a speed setting that is slower orfaster than the actual speed of the master vessel, then the slave vesselwould adjust its speed setting accordingly. Alternatively, the slavevessel can adjust its speed based on relative position to the mastervessel.

Moreover, the slave vessels adjust (at 410) their speeds using feedbackcontrol based on deviation from required inline positions of thecorresponding slave vessels.

Note that if a limit violation (such as violation of one of theconstraints discussed above) should happen on one or more of the slavevessels, the master vessel is informed of this limit violation, suchthat the master vessel can perform an adjustment of its limits andtherefore the speed setting of the master vessel accordingly. Thecommunication of the limit violation can be performed manually orautomatically.

In a more advanced embodiment, all vessels can have feedforwardcontrollers from constraints on the other vessels as well as constraintsof the particular vessel, so that speed setting adjustments areperformed simultaneously and automatically on all vessels. In thismanner, a single software package can be executed on each of the vesselsto perform independent control of the vessels. In yet anotherembodiment, a single computer on one vessel can be used to control allvessels of a multi-vessel arrangement.

Optionally, information relating to tension of a streamer (110 or 111)can be monitored by a control system according to an embodiment. Notethat information relating to tension of a streamer is one input to afeedforward controller as discussed above. Information relating to thetension can be monitored to automatically warn the crew of a vessel of apotentially dangerous situation, where tension on a streamer exceedssome predefined threshold. Not only can the speed of a vessel beadjusted based on tension of a streamer, as discussed above, an alarmcan also be automatically generated to warn the crew of a potentialproblem such that the crew can intervene if the crew deems it necessary.

In some implementations, one or more of the vessels can also be providedwith cross-line controllers to maintain cross-line positions of thevessels with respect to each other. The cross-line direction isperpendicular to the inline direction of a vessel, which is thedirection in which a vessel is traveling. The cross-line controller cantake as input information relating to the inline speed control. In someimplementations, the inline controller and cross-line controller may becombined together such that constraints on one will be constraints onthe other.

Information regarding the speed of the vessel can also be provided to acontrol system that controls activation of seismic sources, such as airguns, vibrators, and so forth. The speed information can be used by thecontrol system to control or predict the appropriate activation timesfor the seismic sources.

FIG. 6 shows an example computer in which control software 502 accordingto some embodiments is executable. The control software can be executedon one or more central processing units (CPUs) 504. The CPU(s) 504 is(are) connected to a storage 506, where the storage 506 is used to storeinformation relating to constraints 508, information regarding inputs tothe feedforward controller discussed above, and a speed setting 512 ofthe corresponding vessel.

The computer 500 also includes a network interface 514 to allow thecomputer 500 to communicate with remote elements, such as a sensor thatindicates an inline current in the water, a sensor that detects theactual speed of the vessel, sensors indicating tension on streamers, andother devices for indicating information regarding other aspects of theseismic system that may provide constraints on or otherwise affect thespeed of the vessel. The network interface 514 can also be used tocommunicate commands to the corresponding vessel to control the speedand speed setting of the vessel.

In addition to the various uses discussed above, other uses are alsopossible for either the single-vessel context or multi-vessel context.For example, according to at least some of the constraints and inputvariables discussed above, the turn time of a vessel (or vessels) can beminimized or reduced. A vessel can turn from a direction along a firstline to another direction along a second line. Minimizing or reducingturn time refers to minimizing or reducing the amount of time from theend of the first line to the start of the second line.

Also, the techniques discussed above (for either the single-vessel ormulti-vessel context) can also be applied to plan for a vessel (orvessels) to be at the start of a line or at some distance from the startof the line at a given time. This can be useful when there istimesharing between or among vessels in a given region and if otherconstraints apply that restricts the actual shooting time. Yet anotherpossible use is for a user to set a target speed over ground, whichtypically happens when a vessel passes over a particular region, and thevessel has to reduce speed for some amount of time. In a multi-vesselcontext, other vessels would have to reduce speed accordingly.

Instructions of the control software 502 are loaded for execution on aprocessor (such as the one or more CPUs 504). The processor includesmicroprocessors, microcontrollers, processor modules or subsystems(including one or more microprocessors or microcontrollers), or othercontrol or computing devices. A “processor” can refer to a singlecomponent or to plural components.

Data and instructions (of the software) are stored in respective storagedevices, which are implemented as one or more computer-readable orcomputer-usable storage media. The storage media include different formsof memory including semiconductor memory devices such as dynamic orstatic random access memories (DRAMs or SRAMs), erasable andprogrammable read-only memories (EPROMs), electrically erasable andprogrammable read-only memories (EEPROMs) and flash memories; magneticdisks such as fixed, floppy and removable disks; other magnetic mediaincluding tape; and optical media such as compact disks (CDs) or digitalvideo disks (DVDs).

While the invention has been disclosed with respect to a limited numberof embodiments, those skilled in the art, having the benefit of thisdisclosure, will appreciate numerous modifications and variationstherefrom. It is intended that the appended claims cover suchmodifications and variations as fall within the true spirit and scope ofthe invention.

1. A system comprising: multiple marine vessels, wherein each of themarine vessels includes a controller for automatically adjusting a speedof the corresponding marine vessel, wherein the speed of each of themarine vessels is automatically adjusted according to factors thataffect the speed of the marine vessel.
 2. The system of claim 1, whereinthe factors that affect the speed of the marine vessel comprises atleast two of: (1) information relating to tension of at least onestreamer towed by the vessel; (2) information relating to warmup timefor seismic sources; (3) information relating to stability of deflectingstructures of streamers; (4) information relating to minimum timebetween activations of seismic sources; (5) inline water currentinformation; (6) wind speed information; and (7) information regardingrelative position to at least another marine vessel.
 3. The system ofclaim 1, wherein the controller of at least one of the plural marinevessels comprises a feedforward controller that adjusts a speed settingof the at least one marine vessel according to the factors.
 4. Thesystem of claim 3, wherein the controller of the at least one marinevessel further comprises a feedback controller that maintains the speedof the marine vessel according to the speed setting of the marinevessel.